The present invention relates to a road curvature estimating apparatus for estimating a curvature of a road ahead of a vehicle.
Japanese Patent Provisional Publication No. 4-283900 discloses a conventional road curvature estimating apparatus which includes an image device for taking a variable bright density picture of a surface of a road ahead of a vehicle. The picture taken by the image device is supplied to a bright change detecting device so as to obtain the bright change amount of each picture element from a bottom portion to an upper portion of the picture of the image device. The bright change detecting device selects the picture element which has the bright change amount larger than a predetermined amount and is nearest to that of the bottom portion. The picture element obtained at the bright change detecting device is sent to a world coordinate system detecting device to obtain a position of the picture element in an actual world coordinate system. A curve detecting device obtains a curvature and a radius of the road from the actual world coordinate of the bright change element which obtained in the world coordinate system detecting device. The obtained information is supplied to a display device so as to inform a result of the road detected shape to a driver.
However, this conventional curvature estimating apparatus is arranged to take a variable density picture of a road ahead of the vehicle and to execute the coordinate transformation of the curve from the bright change amount. This requires to execute the calculations as to the large amount of picture elements and therefore remarkably increases the time for the calculation. Accordingly, in case that an automatic steering control of the vehicle is executed by utilizing the road curvature estimated by the apparatus, it may happen to generate the delay of the calculation as to a traveling vehicle and to put the control of the vehicle unstable. Therefore, the conventional apparatus is required to compensate the delay by taking the variable density picture of a further distant place of the road. Further, in case that it is necessary to take the variable density picture of the road including a distant place, the picture of a road width at the distant place is represented by a smaller number of the picture elements although the picture of the same road width at the near place is represented by a large number of the picture elements. This degrades the resolution of the picture. Furthermore, since the conventional apparatus is arranged to obtain a line along a road lane such as a white line on the road by means of a polynominal approximation and to calculate the curvature on the basis of the obtained result, the number of the data points of the picture becomes large and thereby increases the time for the calculating process. Therefore, the control of the vehicle may become unstable by the delay of the calculation.